1. Field of The Invention
This invention relates to Mn-Si-Co-Fe-based high-strength brass alloys for sliding members wherein substantially spheroidal crystals of a novel intermetallic compound [Mn,Si,Co,Fe] are formed. The brass alloys have utility in the fields of engine parts, transmission parts, hydraulic parts and vessel parts which are usually employed under severe conditions such as of high temperature and high-speed revolutions, high load and corrosive environments and should have good resistances to wear, seizing and corrosion and also good durability.
2. Description of The Prior Art
As is known in the art, manganese silicide-based high-strength brass castings have been widely used as a sliding member under moderate or high speed conditions or under high load. The wear resistance of this type of alloy relies greatly on the crystals of an intermetallic compound (Mn.sub.5 Si.sub.3). In order to improve the seizing resistance of the manganese silicide-based high-strength brass alloy, there has been proposed a high-strength brass alloy having a low wear resistance and a good seizing resistance wherein Pb is added in large amounts (Japanese Laid-open Patent Application No. 56-11735). For this purpose, there are also used lead bronze alloys such as JIS H5115, LBC-3, LBC-4 and the like.
In recent years, however, manganese silicide-based high-strength brass alloys have been employed in a corrosive environment under sliding conditions with advanced speed and load. Known alloys are not satisfactory with respect to the wear resistance and the durability. This is because the alloys include a crystallized intermetallic compound (Mn.sub.5 Si.sub.3) whose shape is substantially in the form of needles as is particularly shown in FIGS. 4, 5 and 24 and the grains formed at the time of casting are coarse as shown in FIG. 2. Pb is an element which contributes to the improvement of an anti-seizing property and machinability. However, since the known alloys have such crystal structure as set out hereinabove, Pb added in large amounts cannot be uniformly distributed, with the anti-seizing property being not satisfactory. In addition, the alloys have a serious problem on the durability owing to the repeated fatigue during use, coupled with another disadvantage that the known alloys are poor in the corrosion resistance against sea water.
Thus, known manganese silicide-based high-strength brass alloys have not been considered satisfactory with respect to properties when employed, as engine parts, transmission parts, hydraulic parts and vessel parts, under severe conditions such as of high temperature and high speed revolutions, high load and corrosive environment where good wear resistance, anti-seizing property, corrosion resistance and durability are required.
On the other hand, LBC-3 or LBC-4 which is a kind of lead bronze alloy has a good anti-seizing property but is unsatisfactory with respect to the wear resistance. Another problem is that the alloy reacts with lubricating oils, causing corrosion to proceed considerably. Like manganese silicide-based high-strength brass castings, the lead bronze alloys have coarse grains, thus presenting a problem on the durability.